Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.29   10.662%   $58.9718   $58.97   $58.95   $59.00  
  Purchase #2 $193.89   11.616%   $216.4123   $216.41   $216.40   $216.40  
  Purchase #3 $119.26   8.558%   $129.4663   $129.47   $129.45   $129.50  
  Purchase #4 $237.84   7.862%   $256.539   $256.54   $256.55   $256.50  
  Purchase #5 $86.52   13.351%   $98.0713   $98.07   $98.05   $98.10  
  Purchase #6 $150.39   13.627%   $170.8836   $170.88   $170.90   $170.90  
  Purchase #7 $219.90   12.389%   $247.1434   $247.14   $247.15   $247.10  
  7 purchase totals = $1,061.09       $1,177.4877   $1,177.48   $1,177.45   $1,177.50